El Camino Real de Tierra Adentro, the Royal Road of the Interior, is the earliest Euro-American trade route of cultures and commerce in the United States. It spanned about 1,800 miles from Mexico City, where the road originated, to Santa Fe, in New Mexico. For three centuries, this Spanish colonial road followed a network of ancient Native American footpaths and trails that followed the wide expanse of the Rio Grande valley. There were parajes, or campgrounds, along the way for travelers, and early Spanish settlements were established too. Some of the towns and villages are now modern cities, such as Las Cruces, Albuquerque, and Santa Fe. Mexico City, as the former capital of La Nueva España, New Spain, is recognized as a UNESCO World Heritage Center. In 2000, El Camino Real was officially designated as a national historic trail, administered by the US Department of the Interior. In 2005, the El Camino Real International Heritage Center was erected near Socorro, New Mexico. This is an interpretive learning center that presents the history and heritage of the Royal Road in the region as an integral part of Spain's global network of roads and maritime trade routes.